Alloy in Gold and Silver

1. If the gold or silver in your possession is not pure, that is, it is not 100% pure gold or silver, it has some other metal/s mixed to it, such as lead, then the quantity will be the determinant.
2. If the quantity of the silver or gold is more than the alloy, the object will be considered to be gold or silver.
3. Now if this item weighs so much which makes Zakaat waajib, then its Zakaat will be obligatory.
4. If, however, the quantity of the other metal is more, then the object will not be considered to be gold or silver.
5. In this case, the item will be just like any other copper, iron, steel or tin object. Zakaat of gold or silver will not be its ruling.

(Behshti Zewar)